Modern total knee arthroplasty implants replace three separate articulating surfaces within the knee joint: the patello-femoral compartment and the lateral and medial inferior tibio-femoral compartments. Most currently available implants for Total Knee Replacement (TKR) are designed to articulate from a position of slight hyperextension to approximately 115° to 130° flexion. A tricompartmental design can meet the needs of most TKR patients even though the healthy human knee is capable of a range of motion (ROM) approaching 170°. However, there are some TKR patients who have a particular need to obtain high flexion in the knee joint. For many, a TKR that permits patients to achieve a ROM in excess of 130° is desirable to allow deep kneeling, squatting and sitting on the floor with the legs tucked underneath.
Conventional TKR implants do not produce normal knee kinematics or motion and generally have a limited range of motion as compared to that of a normal knee. This is because conventional TKR implants flex by rotating about a generally horizontal axis during flexion and extension, whereas the kinematics of a natural knee joint involves more complex motion of the femur and tibia relative to one another. For example, in a natural knee, the tibia rotates internally about the longitudinal axis of the tibia during flexion.
Although some attempts have been made to design a total knee prosthesis which replicates the kinematics of a natural knee, there exists a room for more improvement.